Strange carb jetting in new bike

[larsbar]

Hello again, I finally got a 1980 XS400SE. It has the third version of the BS34 carbs. I am trying to get the carbs as close to stock as possible as a baseline to begin jetting properly. I can't find any other info about the needle my carbs have, and was wondering if anyone can give me clues on this setup.

I have a 135 main, 42.5 pilot, 271 y-4 needle jet, and a 5gz15 needle on the 3rd clip from the top. The removable jet on the bottom left hole on the back of the carb says 155 on it. The fuel mixture screw is 3 turns out. I have K&N pod filters and stock exhaust.

I am also wondering which needle clip is considered #1. is it the top groove or the bottom?

With these filters should I drill out the plugs to adjust the air screws?

Any info on how close this is to stock, and how this needle compares to stock, will be appreciated very much.

Thanks
Lars

I guess that it wouldn't hurt to add a little intro, it has been a long time since my first.
I am a Mechanical engineering technology student at Camosun college in Victoria BC, Canada. I just about bought this bike almost a year ago, but couldn't get the money together. My plan is to build it into a little two person bobber, just with a longer seat than a normal bobber, like the seats on the 70's trail bikes. For a final project at school I am considering changing it to full electronic controls for the throttle, clutch and shifter. That sure could give it a clean look, no cables, everything inside the handlebars.
Anyway, I have spend a lot of time lurking on here, now I am looking forward to being a more active participant.

 

[62 Jag]

I have an '81 Special and was also confused about my jets being different from the listed ones, but then my Haynes manual was printed in '78 so it doesn't include the later information.

My bike is fairly low mileage and very close to stock except for a pair of Mac mufflers I just installed. It has new stock air filters and I just cleaned out the carbs. It pulls very well I think, much better than it did before with the stock mufflers and seems to want to rev to almost 10k in the gears if I'm not careful.

So, like yours, the mains are 135, pilots are 42.5, the starter air (the one in the intake) is 155 and the throttle plate is 155. Can't tell you about the needles. The pilot air screws are both 4 1/2 turns out. That's where they were when I got the bike and it won't idle at all with much less. The book says 1 to 1-1/4. (There were never any plugs over the pilot screws so I guess a PO removed them.)

 

[OliverB]

AFAIK, you should always turn out the idle air mix screws to 3-3.5 turns out. Just too lean from the factory. Don't know if factory settings were different for Canadian delivered bikes, though.

Keep us posted. Your plans for fly-by-wire controls are intriguing. Would that be safe on a 2-wheeled vehicle?

 

[larsbar]

I wouldn't do fly by wire on the brakes, but I think it is pretty safe, it will just idle or shut off down if power fails, and that is what it does anyway. The clutch I am not sure of, it would be hard to make it safe. It would have to have a default clutch disengaged position to be safe.

Thanks for the replies, not a lot of info on the newer bikes on here, mainly the older carbs, eh?

 

[larsbar]

I got it started, it runs pretty well, pops a little as it returns to idle from higher rpm, but runs pretty well. I will play with it some more.